One attractive paradigm of anticancer strategies is to target oncogenes for sensitization of tumor cells to apoptosis. The rationale is that onco-proteins rely on other factors to maintain homeostasis or promote cancer cell survival. Disruption of one of coordinating proteins would trigger an apoptotic crisis in cancer cells. Oncogenic Ras has been discovered in about 30-40% of human cancers. However, inhibitors targeting mutated Ras have proved not to be effective clinically. Recently, the focus has been on finding signaling pathways that are downstream of or parallel with Ras, and are essential for cancer cells to survive. In the effort to identify the apoptotic partners of mutated Ras, studies showed that loss of PKC, together with mutated Ras, are synthetically lethal in many types of tumors. Recently, we made the novel observation that loss of different PKC isoforms differentially sensitized cells expressing mutated ras to apoptosis. In particular, we identified that co-suppression of PKC ?/ were critical for the induction of apoptosis in cancer cells harboring mutated ras, in which PI3K/Akt function downstream of Ras to mobilized two signaling pathways: one was via upregulating ROS and ER stress-mediated UPR for switching on the apoptotic machinery; and another one was through activating PKC?, resulting in p73 phosphorylation and PUMA/NOXA upregulation. In this renewal application, we will investigate the molecular mechanisms of our novel observation of how Ras, upon loss of PKC ?/, differentially utilizes its downstream effector pathways to selectively sensitize tumor cells to apoptosis, with less or no toxicity to normal cells or surrounding tissues. We will determine how ROS and PKC?/p73 pathways are being redirected by aberrant Ras/PI3K/Akt to activate cell death program after co-suppression of PKC ?/. Thus, the hypothesis to be tested is that upon co-knockdown of PKC ?/, PI3K/Akt are key players in the induction of Ras-mediated apoptosis, which is via perturbing redox homeostasis as well as through activating PKC?/p73-mediated apoptotic network. Accordingly, 4 Specific Aims are formed. Aim 1 will study the mechanisms by which ROS is upregulated in cells expressing aberrant ras or PI3K/Akt upon co- suppression of PKC ?/. Aim 2 will determine the mechanisms by which ROS induces ER-stress/UPR activation in cells expressing aberrant ras or PI3K/Akt upon co-suppression of PKC ?/. In Aim 3, we will determine the role of p73 in the sensitization of cells expressing aberrant ras or PI3K/Akt to apoptosis after co- knockdown of PKC ?/. In Aim 4, we will determine the pro-apoptotic effect in cells expressing aberrant ras or PI3K/Akt in vitro and in vivo after co-suppression of PKC ?/. The outcomes of our research will reveal molecules involved in this synthetic lethal interaction between Ras mutations and loss of PKC ?/, which will provide the potential information for designing more effective drugs to treat human cancers harboring aberrant ras or PI3K/Akt.